Referring to FIG. 1A, a conventional transflective LCD panel 10 of MTN (Mixed Twisted Nematic) mode is shown to include an upper polarizer 12, an upper glass substrate 14, an upper electrode 16, a liquid crystal layer 18, a lower electrode 20, a lower glass substrate 22 and a lower polarizer 24. When the transistor in the LCD panel 10 is switched on (i.e. when a voltage is applied onto opposite ends 16, 20 of the liquid crystal layer 18), an electric field will be induced, and extends parallelly to the upper and lower electrodes 16, 20. Since the phase difference between the upper and lower polarizers 12, 24 is 90°, the light beams passing through the lower polarizer 24 will be reflected from an upper surface without changing their direction so as to be perpendicular to the upper polarizer 12. Under this condition, the orientation of the liquid crystal molecules in the liquid crystal layer 18 changes from the state shown in FIG. 1B into that shown in FIG. 1A, and extends parallel to the electric field. Since the light beams cannot pass through the upper polarizer 12, black spots can be seen on the display screen.
When the transistor of the conventional LCD panel 10 is switched off (i.e. when no voltage is applied onto opposite ends 16, 20 of the liquid crystal layer 18), as shown in FIG. 1B, the orientation of the liquid crystal molecules in the liquid crystal layer 18 maintains in their initial alignment such that the light beams passing through the lower polarizer 24 will pass through the liquid crystal layer 18 and the upper polarizer 12. Thus, white spots will be formed on the display screen.
One drawback of the aforesaid conventional t transflective LCD panel 10 resides in that not all the liquid crystal molecules in the liquid crystal layer 18 extend parallelly to the electric field when voltage is applied thereon, thereby lowing the contrast ratio and consequently forming uneven distribution of brightness throughout the entire length thereof. In addition, it takes longer response time to perform the transition from their initial alignment to the displayable alignment.
In order to solve the above-stated drawbacks, in 1996 Fujitsu had proposed a Vertical Alignment system, in which an alignment member or film can be fabricated on the upper and lower electrodes to assist to change the orientation of the liquid crystal molecules in the liquid crystal layer with respect to the upper polarizer without voltage applied thereon. The light beams therefore cannot penetrate through the upper polarizer. When a voltage is applied onto the liquid crystal layer, the liquid crystal molecules make a 90° turn, thereby permitting the light beams to pass through the upper and lower polarizers. The VA system thus shortens the response time, causes an increment to the contrast ratio and helps to eliminate the drawbacks of MTN system. However, the transflective LCD panel of Vertical Alignment mode suffers from a viewable problem. For example, the user sees blue color when he is right in front of the display screen (see FIG. 2A), which means that when half voltage is applied onto the liquid crystal layer, the liquid crystal molecules turn only half way from their initial position. If he moves further right about 10 cm, he is generally aligned with the orientation of the liquid crystal molecules so that he will see white color, not the blue color.
Referring to FIG. 2B, in order to solve the viewable problem encountered during use of the conventional transflective LCD panel of VA mode, the transflective LCD panel 40 of MVA (Multi-domain Vertical Alignment) mode is proposed, and includes upper and lower glass substrates 26,28, and upper and lower electrodes 32,34. A plurality of projections 36 are fabricated on the upper and lower electrodes 32,34 so as to divide each of the pixel units into multi-domains. Under this condition, the liquid crystal molecules forming the patterns will be symmetrically disposed along the front-to-rear line such that the user standing right in front of the display screen will see the same color regardless of his viewing angle with respect to the display screen.
The LCDs can be constructed in a relatively compact size and are used in mobile phones and PDA (personal digital assistant) due to the rapid advance of TFT (Thin Film Transistor) or LTPS (Low Temperature Poly-Silicon) technique in addition to its lower power consumption and low radiation. Note that the LCDs itself are not light emitting instruments, and each requires a backlight module in order to display images and information on the display screen. When the LCD is used outdoor, the ambient light is so strong that the reflection of sunlight from the surface of the display screen overwhelms any light coming through the LCD panel. Most of today's LCDs are constructed to be tranflective in order that the display screen can be illuminated by combination of the backlight and the ambient light.